Electrical control circuitry for burners



Ap 1968 P. GIUFFRIDA ETAL 3,376,099

ELECTRICAL CONTROL CIRCUITRY FOR BURNERS 5 Sheets-Sheet 1 Filed March30, 1966 N Om A ril 2, 1968 P. GIUFFRIDA ETAL 3,376,099

ELECTRICAL CONTROL CIRCUITRY FOR BURNERS 3 Sheets-Sheet 2 Filed March30, 1966 m m mwmm a w ..l r I ..w 5/

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ELECTRICAL CONTROL CIRCUITRY FOR BURNERS Filed March so, 1966 3Sheets-Sheet 5 I02 I=-1 0 I04 W [F IG. 5,

United States Patent Oflice 3,376,099 Patented Apr. 2., 1968 3,376,099ELECTRICAL CONTROL CIRCUITRY FOR BURNERS Philip Giulfrida, NorthAndover, and Phillip J. Cade,

Winchester, Mass, assignors to Electronics Corporation of America,Cambridge, Mass, a corporation of Massachusetts Filed Mar. 30, 1966,Ser. No. 538,713 6 Claims. (Cl. 431-26) ABSTRACT OF THE DISCLOSURE Acombustion control system includes a main control relay; an ultravioletradiation sensor andelectronic circuitry connected to the sensor foroperating a flame relay; fuel control elements and an ignitiontransformer; a time delay relay; a safety lockout switch; and a timedelay switch having a bimetallic actuator heated by a heater connectedto a 0.2 volt source. When the system is energized the electroniccircuitry connected to the sensor is immediately energized. A set ofnormally closed flame relay contacts, a set of normally closed safetylockout switch contacts, and a set of normally open time delay switchcontacts are connected in the energizing circuit of the main controlrelay. After a short time interval the time delay switch contacts closeand the main control relay is energized to start a combustion cycle.However, if the electronic circuitry causes the flame relay to beimmediately energized, the control relay circuit is interrupted so thatcombustion cannot be initiated. In the combustion cycle the time delayrelay is energized and after a predetermined interval the ignitiontransformer is de-energized by that relay and cannot be againre-energized until the main control relay has been de-energized.

This invention relates to electrical control circuitry and moreparticularly to control circuitry particularly adapted for use incombustion supervision systems and to improved components for use insuch circuitry.

In conjunction with the safe operation of combustion systems it isdesirable to provide a controller which automatically programs theoperation of a fuel burner to initiate the desired combustion conditionin the system and then to supervise on a continuing basis thatestablished combustion condition. It is an object of this inven tion toprovide novel and improved apparatus for use in such programming of fuelburners and for supervision of combustion conditions established by suchfuel burners.

Another object of the invention is to provide a novel and improvedarrangement for checking in a coordinated and reliable manner the properoperation of a flame sensor prior to initiating the fuel burningsequence.

Another object of the invention is to provide a novel and improvedcircuit arrangement which provides protection against unwanted recyclingof the fuel burner systern after occurrence of a flame failurecondition.

Still another object of the invention is to provide novel and improvedcontrol components which impart a time delay in an operating sequenceand which are particularly useful in combustion supervision systems.

Other objects, features and advantages for the invention will be seen asthe following description of a particular embodiment thereof progresses,in conjunction with the drawings, in which:

FIG. 1 is a schematic diagram of a combustion control system constructedin accordance with the invention;

FIG. 2 is a side elevational view of a lock-out switch structureemployed in the circuitry shown in FIG. 1;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2 showingdetails of the lock-out switch in a first (lock-out) position;

FIG. 4 is a sectional view similar to FIG. 3 showing details of thelock-out switch in a second (normal) position;

FIG. 5 is a top elevational view of another electrical control elementemployed in the circuitry shown in FIG. 1; and

FIG. 6 is a front elevational view of the control circuit element shownin FIG. 5

The system shown in FIG. 1 has terminals 10, 12 for connection to asuitable source of electric power. A transformer 14 having a primarywinding 16 and a secondary winding 18 is connected directly acrossterminals 10 and 12. Also connected directly across those terminals arecontrol circuitry for an ignition control element 20, a blower controlelement 22, a pilot fuel control element 24 and a main fuel controlelement 26-. In addition the control circuitry includes a time delayelement 28 that controls normally closed contacts 281.

The secondary winding 18 of the transformer has a lower terminal 36, afirst tap at twelve volts to which line 32 is connected, a second tap attwenty volts to which line 34 is connected, and an upper terminal 36which is at 580 volts. An auxiliary tap provides a potential differenceof 0.2 volt and line 38 is connected to it for energizing a controlelement 40 that is connected across lines 34 and 38.

Transformer secondary output voltage is connected through capacitor 42and resistor 44 to a flame sensor 46. This flame sensor in the preferredembodiment is an ultraviolet detector of the Geiger-Mueller type.(Elements 44 and 46 may be located at a remote location, for example inthe wall of a combustion chamber that is to be supervised.) The sensor46 is connected to inductor 50 having output lines 52, 54 connectedthrough diodes 56 and a tap 58 connected to the common bus 30. Thediodes 56 are connected together at common junction 60 which in turn isconnected through resistor 62 to an amplifier circuit includingtransistors 70 and 72. Transistor 72 has coil 74 of a flame relayconnected in its collector circuit. That flame relay controls contacts74-1, 74-2, 74-3 and 744. This transistor amplifier circuit is energizedby electric potential that is applied on bus 76 through diode 78 fromline 34 connected to the twenty volt tap of the secondary winding 18.

Connected to the transformer secondary, in addition to the flamedetector circuitry, is a main control circuit includes a main controlrelay 80 which controls contacts 804, 802 and 80-3. The control circuitincludes, in addition, a control device such as a thermostat 82connected in series with the control relay coil 80 and a lockout switchactuator 84 that controls contacts 841. This control circuitry isenergized through a delay switch 40-1 that is physically mounted on theheater 40 (as indicated in FIGS. 5 and 6) and when that switch isclosed, energization of the main control relay 80 is enabled.

When power is applied to terminals 10, 12, the secondary of transformer14 is energized. The flame detection circuitry is immediately energizedbut a delay in energizing the control circuitry is imposed by the delaycontrol 49, 40-1. With reference to FIGS. 5 and 6, electric circuitelement 40 has terminals 90, 92. Terminal 96' is securely mounted infixed position by mounting bracket 94 and has projecting upwardly fromit a bimetallic element that includes a wide main portion 96 and narrowstrip 98. Strip 98 extends downwardly to flexible link 3100 on which acontact member 102 is mounted. Cooperating with contact member 102 andin juxtaposition therewith is a second contact member 104.

Electric current flows through bimetallic element 40 when thetransformer is energized and narrow leg 98 flexes under the greaterheating to which it is subjected and moves the contact 102 into electriccircuit completing relationship to contact 104 after a short time delay.The proportioning of the wide and narrow legs 96, 98 of the bimetallicprovides thermal compensation for changes in ambient temperature. Itwill be seen with reference to FIG. 1 that the bimetallic element 40 iscontinually energized as there is 0.2 volt impressed across it wheneverthe transformer secondary 18 is energized. Thus this simple circuitcomponent provides an initial delay (a typical value being in the rangeof 3-10 seconds) in the energization of the control circuitry butsubsequent to that initial delay this component continuously maintainsthe control circuitry in energizable condition as long as power isapplied to terminals and 12. Also, should the transformer bedeenergized, switch -1 resets rapidly as it is physically mounted on thebimetallic element that is directly heated by electric flow and there isno thermal mass of an auxiliary heater to delay reset.

This delay in energization of the control circuitry provides a check onthe proper operability of the flame detection circuitry. It will be seenthat the flame detection circuitry is energized immediately uponenergization of the transformer secondary and that the control circuitis not energized until contacts 102, 104 close. Should the flamesupervision circuitry not be properly operative, for example due to adefective (e.g. continuously avalanching) sensor tube 46, contacts 74-2will open and thus prevent energization of control relay 80 in responseto a request by control element 82.

Provided the flame detection circuitry is in proper operating condition,however, contacts 74-2 remain closed at this time as there is no flamein the supervised combustion chamber and on closing of contacts 102,104, the control relay 80 will be energized on call for heat by thethermostat 82 or other control element. Upon energization of relay coil80 contacts 80-2 close and completes a holding circuit for relay 80 vialine 32 connected to the twelve volt tap. It will be noted that thisholding circuit is independent of the heater element 84 of the safetylock out device. The heater 84 remains energized however as it isconnected across eight volts between lines 32 and 34 through contacts40-1, the now closed flame relay contacts 74-2 and the control relaycontacts 80-2. This circuit maintains the lock out switch heater 84energized until detection of flame causes pick up of relay 74.

Also, energization of the control relay coil 80 causes contacts 80-3 toclose and energizes the ignition control unit 20, the blower controlunit 22 and the pilot fuel valve control unit 24. This establishes anignition condition in the combustion chamber and fuel is supplied tothat chamber through the pilot valve. As soon as ignition occurs andflame is detected in the combustion chamber by sensor 46 a signal isproduced by the flame sensing circuitry to energize relay coil 74.Contacts 74-1 and 74-4 close and contacts 74-2 and 74-3 open. TheOpenings of contacts 74-3 deenergizes the ignition control device whilethe closing of contacts 74-4 energizes the main fuel control unit 26 sothat fuel from the main fuel line flows into the combustion chamber toestablish the main flame which is continually supervised by the sensor46. Independently of the establishment of the main flame but normally ashort time (a typical total time delay being ten seconds) subsequentthereto the timing control 28 operates to open contacts 28-1 anddeenergize the pilot fuel cont-r01 element 24. (Thiscircuit arrangementthus proves main flame by shutting off the pilot flame automatically andfurther prevents reignition of pilot flame after flame failure exceptafter manual restart (reset of the lockout switch 84).) The apparatus isnow in operative condition with the control relay and the flamedetection relay 74 in energized condition and the thermostatic device 82indicat: ing a continued operation of the burner.

As soon as the thermostatic device 82 no longer indicates the need foroperation of the burner, its circuit wall open and deenergized thecontrol relay 80. With that occurrence, contacts 80-3 will open and themain fuel control element 26 will be deenergized. With the terminationof fuel flowing into the combustion chamber flame will cease and theflame relay 74 will be deenergized so that the entire controlledapparatus will be shut down but ready for another operating cycle uponthe closing of the thermostatic device 82.

Should flame failure occur during an operating cycle however, such thatrelay 74 is deenergized, the fuel flow is immediately interrupted by theopening of con: tacts 74-4, and the safety lock out heater 84 isenergized with the closing of contact 74-2 so that after a predeterminedlength of time that heater will cause the contacts 84-1 to open anddeenergize the main control relay coil 80, shutting down the controlledapparatus and requiring manual reset of switch contacts 84-1 before theapparatus again. Also, should the flame relay 74, after completion of anoperating cycle, failto open contacts 74-1 upon termination of flame inthe cumbustion chamber, the safety lock out heater will be energized bya circuit completed from line 34 through the safe start contacts 102,104, contacts 74-1 that remain closed and contacts 80-1 which are nowclosed. Heater element 84 will be heated sufliciently to cause thecontacts 84-1 to open (after a delay typically in the order of 6-9seconds) and in open condition will prevent re-energization of the relaycoil 80, resulting in safe shut down of the controlled apparatus.

The structure of the lock out switch unit 84 may be seen with referenceto FIGS. 2-4. That switch unit controls contacts 84-1 which includescontact elements and 112. Each contact element is mounted on a flexible,electrically conductive leaf 114 that has a terminal element 115, 117respectively and each leaf has an upper end 116 against which anactuator surface 118, 120 re spectively acts. The contact elements aremounted in fixed position on the body of the lock out unit. Projectingupwardly from that body is a post member 124 and above that member anactuator element in the found plunger 126 which carries actuator surface120. Interposed between the post member and the actuator element is asleeve element 128 which carries the projection 118 and is disposed forsliding movement. A first biasing spring 130 acts between the unit body122 and the sleeve 128 to urge sleeve 128 upwardly while a secondbiasing spring 132 acts between plunger 128 and the post 124 to urge theplunger 126 to its upper (normal) position.

The contact actuator sleeve has secured to it at its lower end a latchmember l40 which cooperates with an adjustable latch member 142 mountedon a bimetallic sheet heater element 84. The configuration of thebimetallic element 84 may be best seen with reference to FIG. 2. Thatbimetallic element has two terminals, 146, 148 and a serpentineconductive path from terminal 146 is provided through a first set 154 ofthree narrow sections connected in series through an intermediate bridgeportion 150 that carries a depending leg 152 to a second set .154

of three narrow sections connected in series and then to terminal 146.The depending leg 152 carries the adjustable latch member 142. Anon-conductive bridging element 156 is disposed at the upper end of eachset 150, 154 to assure the flexing of the sheet as a unit at thosepoints.

In operation, the lock out switch is set into the posi tion shown inFIG. 1 by depressing the actuator 126. This compresses springs 130 and132 moving both the contact engaging surfaces 118, 120 downwardly andflexing the contact support structures outwardly away from the body 122of the switch unit as the intermediate (sleeve) member 128 is moveddownwardly to the latched position. Upon release of actuator 126, theactuator moves upwardly under the influence of spring 132 but theintermediate member 128 is held in latched condition in the positionshown in FIG. 4 so that contacts 110 and 112 are in circuit completingengagement. The lockout switch structure will remain in this positionuntil the heater 84 has been subjected to sufficient electrical currentflow to cause the latch member 142 to move outwardly and release thelatch element 140. When that occurs spring 130 moves sleeve 126 upwardand the switch components return to the position shown in FIG. 3 andremain in that position until the lock out switch is reset by manuallydepressing actuator 126. It will be seen that this lock out switchstructure provides a compact, reliable and relatively inexpensivearrangement that includes thermal compensation provided by leg 152 forambient temperature conditions.

While a particular embodiment of the invention has been shown anddescribed, various modifications thereof will be apparent to thoseskilled in the art and therefore it is not intended that the inventionbe limited to the disclosed embodiment or to details thereof anddepartures may be made therefrom within the spirit and scope of theinvention as defined in the claims.

What is claimed is:

1. Burner control apparatus for use with a fuel burner installationhaving an electrically energizable main fuel control valve, anelectrically energizable pilot fuel control valve, and ignition meansoperative when energized to ignite fuel at the burner, comprising acontrol relay having a plurality of normally open switches which areclosed upon energization of the apparatus in response to a request forinitiation of flame in the fuel burner,

flame sensing means adapted to sense the presence of flame in the fuelburner and having a normally closed switch which is opened upon thesensing of flame and a normally open switch which is closed upon thesensing of flame,

checking means having a normally closed check switch and a time delayedactuator effective after a time period of energization thereof to opensaid check switch,

first circuit means including one of said control relay switches andsaid normally closed flame sensing means switch and adapted to energizethe ignition means,

second circuit means including one of said control relay switches andsaid check switch and adapted to energize said pilot fuel valve,

third circuit means including one of said control relay switches andsaid normally open flame sensing means switch and adapted to energizesaid main fuel control valve, fourth circuit means including one of saidcontrol relay switches and said checking means actuator and adapted toenergize said checking means actuator,

said third circuit means maintaining said main fuel control valve inenergized condition only in response to the continuing sensing of flamein the fuel burner,

and said checking means actuator opening said check switch anddeenergizing said pilot fuel control valve after a time period ofenergization of said checking means actuator independently of thesensing of flame in the fuel burner and holding said check switch openand said pilot fuel control valve deenergized until said control relayis deenergized,

a fifth circuit including the coil of said control relay,

a sixth circuit including said flame sensing means,

Cir

means connecting said fifth and sixth circuits to a common electricalenergy source, and means to delay energization of said fifth circuitincluding a circuit element arranged for movement in response to flo-wof electric current through it connected to said common electricalenergy source and a circuit completing element connected in said fifthcircuit and physically mounted on said circuit element for movementtherewith, said circuit completing element delaying energization of saidfifth circuit until said flame sensing means has been energized.

2. The apparatus as claimed in claim 1 wherein said flame sensing meansincludes a second normally closed switch which is opened upon thesensing of flame, said flame sensing means switch being connected insaid fifth circuit so that said second flame sensing means switchprevents the energization of said control relay should said second flamesensing means switch be opened before said circuit element closes saidfifth circuit.

3. The apparatus as claimed in claim 2 wherein said circuit element is abimetallic element having one portion of said circuit completing elementphysically mounted on it.

4. The apparatus claimed in claim 3 and further including means to applya fraction of a volt continuously across said circuit element.

5. The apparatus as claimed in claim 4 and further including a safetylockout switch having a pair of electric circuit completing elementsforming a normally closed switch and a bimetallic time delay actuatormember effective after a period of energization to open said lockoutswitch, a manual operator for placing said elements in a firstelectrical circuit control condition, means urging said elements towardsa second circuit control condition, and latch means mounted on saidbimetallic member for securing said circuit elements in said firstcondition, said latch means releasing said contact elements from saidfirst condition upon movement of said bimetallic member.

6. A combustion control system comprising a main control relay forcontrolling the operation of a burner,

a flame detector circuit including a flame relay,

a circuit responsive to demand for burner operation for energizing saidmain control relay including a normally closed contact controlled bysaid flame relay,

and a voltage source for energizing said main control relay energizingcircuit and said flame detector circuit,

characterized by the provision of means to delay the energization ofsaid main control relay energizing circuit including a bimetalliccircuit element connected to respond to electric current flow forenergizing said flame detector circuit,

a tap connected to said voltage source for continuously applying afraction of a volt across said bimetallic element,

and a circuit completing element physically coupled to said bimetalliccircuit element for delaying the completion of said main control relayenergizing circuit until after said flame detector circuit has beenenergized.

References Cited UNITED STATES PATENTS 2,440,700 5/ 1948 Rosche 15-8-282,662,591 12/1953 Hanson 158-28 2,727,568 12/1955 Smith 158-28 2,751,9726/1956 Loeber 15828 2,989,117 6/1961 Graves 15828 JAMES W. WESTHAVER,Primary Examiner.

